cve 230 lab report 3

CVE 230 Mechanics of Materials

Lab Report #2b

Testing of Hardened Concrete

March 28, 2013

LAB REPORT #1

TESTING OF FRESH AND HARDENED CONCRETE

Introduction:

The main objective of this lab was to analyze the compressive and tensile properties of concrete by executing various tests on different concrete specimens created by the students. There were three tests that the students had to conduct in this lab: a compression test, a flexure test, and the non-destructive test. The compression test was done on the cylinder, as well as the split cylinder test. The

Prepared by Juan Villa

Fresh concrete is used in various ways in today’s world. Fresh concrete can be seen in almost every

civilized city in the world. We use fresh concrete for different functions such as constructing

buildings, bridges, roads, etc. As a civil engineer, it is essential to know the technicalities of fresh

concrete and all of its characteristics and processes. Concrete is anattachedcompanion to a civil

engineer and in this lab we will get a small taste as to what the actual process of making concrete is.

In this lab, the students would be exposed to process involved when making fresh concrete, from

scratch. All of the necessary components for creating concrete were provided to the students and

specific instructions on how to make the concrete we also provided. A large amount of concrete was

created in this lab in order to provide a good amount for different future tests. These tests included a

compression tests, rebound hammer test and a split cylinder test. Overall, the students were exposed

to various methods that are involved when making concrete, testing concrete over an elongated

period of time, and making conclusions about the tests.

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flexure test was done in order to determine the modulus of rupture. The non-destructive test was executed using the Schmidt hammer.

Materials and Methods:

The proportions used for the making of the concrete are as follows: 59.6lbs of coarse aggregate, 48lbs of fine aggregate, 24.6lbs of cement, and 12lbs of water. The concrete that was made was mixed on the first day of the 3 week period. Compression tests were carried out on two 4x8 cylinders after 7 and 14 days of hardening and a split cylinder test was performed on another cylinder after allowing the cylinder to cure for 28 days. The specimens that were made included several batches 4x8 (in) concrete cylinders that the students had created. The specimens were cured by placing them in the small bath tub for 7, 14, 28 days respectively for testing.

a. Compressive Strength

Briefly describe the test, when was it made (7 days, 14 days, 28 days), provide a short table with the failure load for each of these tests.

Compression tests were executed on the 4x8 cylinders after seven and fourteen and twenty eight days of hardening. The compression tests were performed by placing the already-made 4x8 cylinders a machine that provided applied loads on the cylinders. These machines would provide a number for the failure load for each cylinder. All of the failure loads for each different week were recorded.

The compressive strengths were then calculated by using the cross sectional area measured from the cylinders. The calculations were conducted just as those from the compression tests.

Time (Days) Failure Load (ksi)7 2114 3628 48

b. Tensile strength

b1. Modulus of rupture test: the load that caused failure of the beam.

Modulus of Rupture Test:

During the rupture test, the geometry of each specimen was measured and recorded as loaded. The widths and depths of each section in the mid third were recorded as well. The average of the several readings was additionally recorded as well. The test was then executed as explained by TA. The failure load was observed and recorded.


LAB REPORT #1


The load that caused failure to the beam was 7880psi.

b2. Split cylinder test:

Describe the test as well as the load that caused failure.

The split cylinder test was performed in the same manner in which the compression test, the only difference was that the split cylinder test, as the name tells it, required the cylinder to be on one of its sides, causing a splitting down the middle of the specimen

• The 6"x6"x20" specimen was placed on its flat side on a solid and smooth floor area. The five readings were recorded by the TA for each specimen. The average rebound measurement was then calculated. Using the calibration chart, the compressive strength of the specimen was also approximated. The specimen used will also be used for the modulus of rupture test in the future.

The load that caused failure was 48kips.

c. Non-destructive test

The non-destructive test is used for various things, but our main use of this test was to approximate the strength of in-situ concrete. The non-destructive test is used with a rebound hammer. The rebound hammer can provide us with a reading for the specific strength of the concrete being tested. It can be used on different types of concrete in order to compare respective strengths. The principle behind the method is for us to be able to measure compressive strength of the specimen without the use of a physical load on the specimen being tested. The accuracy of the rebound hammer is about ±25% within the range of the values that a destructive test would provide.

d) Modulus of elasticity of concrete. Discuss the method, i.e. you calculate the unit weight of your concrete and then use a ACI formula to get EEc = w1.5√ fc ' (psi)

where w = unit weight (pcf) = 140.6pcf

90 pcf < WC<155 pcf

Ec =1401.5√4,000 (psi)

Ec = 3.48e-6 psi

Sketch:


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Results and Discussion:

Results and Discussion

a. Compressive Strength:

Plot of Compressive strength vs. Time.

Time Force (psi) Compressive Strength (ksi)

7 21 1.6714 36 2.8628 48 3.82


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5 10 15 20 25 300

0.51

1.52

2.53

3.54

4.5

Time vs Compressive Strength Plot

Time (Days)

Com

pres

sive

Stre

ngth

(ksi)

As expected, the longer the days, the greater the failure loads on the specimen. This means that the relationship between the failure load and the days passed was directly proportional in our case. As shown in the time vs. compressive strength plot, the failure load amount increased simultaneously and relatively with the days that passed.

The progression of the strength in time shown in the plot demonstrates that as time goes on, the concrete becomes stronger and can withstand a bigger load. For example, during the 7th day, the strength that the specimen could withstand was of 1.67ksi before it could crumble, but during the 28th day, the specimen was strong enough to withstand 3.82ksi before crumbling. This relationship between time and strength was expected.

b. Tensile strength.

Formula used to get the modulus of rupture:

fr = PL/bh2

= (7880) (20)/ (6*62)

Actual value: Fr = 729.64psi

How does it compare with ACI formula?

ACI formula: fr = 7.5 √ f c ‘( psi)


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= 7.5√(4000)

=474.34psi

The value of the ACI formula, 474.34psi, was lower than the actual value of 729.63psi. which is what we expect before the calculations are performed.

Did the beam break in the mid-third? (If not we are supposed to repeat the test).?

The cylinder did split down the middle.

Formula for the split cylinder strength and the value calculated:

Split Cylinder Test

fct = 2P/pi*l*d

=(2*5,140)/(pi*12*6)

Fct = 45psi

ACI formula: fct = (5 to 7) √ f c ‘( psi)

= 6 √4,000 (psi) ?

=379.47psi

The actual value was calculated to be 45psi, and the value calculated from the ACI formula was 379.47psi. the disparity between the values might have resulted from the inconsistency of the procedure followed when using the machine, or by the clarity of the reading scales.

How do the two different ways to find the tensile strength compare? Which one you would trust more for your calculations and why?

The rupture test to me is the better one, in my opinion, because this test is more adequate for beams. The cylinder test is the better one for columns because you are testing the beam in compression.


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c. Nondestructive testing.

@-90o and 25 the cylinder compressive strength is roughly 2,700psi, this is the average reading because we only took one reading.

The line used was the 25 line, and the angle used was -90o

e) Modulus of elasticity.

Provide the formula and the calculation:

Ec = w1.5√ fc ' (psi)

where w = unit weight (pcf) = 140.6pcf

90 pcf < WC<155 pcf

Ec =1401.5√4,000 (psi)

Ec = 3.48e-6 psi


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Would you characterize this as normal weight concrete?

The unit weight calculated was 140.6pcf and the normal unit weight of concrete is 145pcf so these two values are extremely close to one another.

Conclusions:

The compression tests were by far the most important test of this experiment. The results from these tests were what determined the relationship between the time and the allowable compressive strength of the concrete. The tensile tests were also important because they gave us an output when executing both a split cylinder test and a modulus of rupture test. These tests also provided measurements for the failure loads that occurred at each test, something that engineers and construction companies must do on a daily basis in order to provide the world with the strongest and most durable concrete available.

The concrete that the students created was very well suitable for the purpose of this lab. The concrete tests were able to be carried out successfully and consistently. Some factors that might have affected the results could include having the proper and exact ratios when making the concrete, the curing process which we had no control over, as well as the consistency of the machines used in the tests


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Appendix

Calculations:

Schmidt Test:

Angle: 900 ; f’c: 2,700psi

Rebound Test:

Weight: 8.18lbs; Vol: pi*r2h = pi(22)(8) = 100.53 psi Unit Weight = W/V = 8.18/100.53 = 0.0813 convert to pcf

Rupture Test:

Fr = fct = PL/bh2

= (7880) (20)/ (6*62)

Fr = 657psi

Compression Test:

f’c = 48,000/A

f’c= 4,000psi

Split Cylinder Test

fct = 2P/pi*l*d

=2*5,140/pi*12*6

Fct = 45psi


cve 230 lab report 3

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